1. Market
US: a rather unified single English-speaking market of 300 million people.
EU: 27 different markets in the EU + half a dozen markets in countries freely associated with the EU (e.g. Norway and Switzerland) in different languages, cultures and expectations
2. Money
US: unlimited unchecked runaway money. All the "unicorns" we keep hearing about can easily lose hundreds of millions and even billions dollars a year for decades, and still considered a success
EU: less money, and you are expected to actually turn a profit at some point